1. Industrial Applicability
The present invention finds applicability in the transportation industries, and more specifically private and commercial vehicles. Of particular importance is the invention""s incorporation into hybrid electric vehicles.
2. Background Art
Generally, a hybrid electric vehicle combines electric propulsion with traditional internal combustion engine propulsion to achieve enhanced fuel economy and/or lower exhaust emissions. Electric propulsion has typically been generated through the use of batteries and electric motors. Such an electric propulsion system provides the desirable characteristics of high torque at low speeds, high efficiency, and the opportunity to regeneratively capture otherwise lost braking energy. Propulsion from an internal combustion engine provides high energy density, and enjoys an existing infrastructure and lower costs due to economies of scale. By combining the two propulsive systems with a proper control strategy, the result is a reduction in the use of each device in its less efficient range. Furthermore, and as shown in FIG. 1 regarding a parallel hybrid configuration, the combination of a downsized engine with an electric propulsion system into a minimal hybrid electric vehicle results in a better utilization of the engine, which improves fuel consumption. Furthermore, the electric motor and battery can compensate for reduction in the engine size.
In typical configurations, the combination of the two types of propulsion systems (internal combustion and electric) is usually characterized as either series or parallel hybrid systems. In a pure series hybrid propulsion system, only the electric motor(s) are in direct connection with the drive train and the engine is used to generate electricity which is fed to the electric motor(s). The advantage of this type of system is that the engine can be controlled independently of driving conditions and can therefore be consistently run in its optimum efficiency and low emission ranges. A key disadvantage to the series arrangement is the loss in energy experienced because of the inefficiencies associated with full conversion of the engine output to electricity. In a pure parallel hybrid propulsion system, both the engine and the electric motor(s) are directly connected to the drive train and either one may independently drive the vehicle. Because there is a direct mechanical connection between the engine and the drive train in a parallel hybrid propulsion system, less energy is lost through conversion to electricity compared to a series hybrid propulsion system. The operating point for the engine, however, can not always be chosen with full freedom.
The two hybrid propulsion systems can be combined into either a switching hybrid propulsion system or a power-split hybrid propulsion system. A switching hybrid propulsion system typically includes an engine, a generator, a motor and a clutch. The engine is typically connected to the generator. The generator is connected through a clutch to the drive train. The motor is connected to the drive train between the clutch and the drive train. The clutch can be operated to allow series or parallel hybrid propulsion.
A power-split hybrid system, as is exemplarily employed with respect to the present invention, includes an engine, a generator and a motor. The engine output is xe2x80x9csplitxe2x80x9d by a planetary gear set into a series path from the engine to the generator and a parallel path from the engine directly to the power train. In a power-split hybrid system, the engine speed can be controlled by varying the power split to the generator by way of the series path, while maintaining the mechanical connection between the engine and drive train through the parallel path. The motor augments the engine on the parallel path in a similar manner as a traction motor in a pure parallel hybrid propulsion system, and provides an opportunity to use energy directly through the series path, thereby reducing the losses associated with converting the electrical energy into, and out of chemical energy at the battery.
In a typical power-split hybrid system, the generator is usually connected to the sun gear of the planetary gear set. The engine is connected to the planetary carrier and the output gears (usually including an output shaft and gears for interconnection with the motor and the wheel-powering, final drive train) are connected to the ring gear. In such a configuration, the power-split hybrid system can generally be operated in four different modes; one electric mode and three hybrid modes.
In the electric mode, the power-split hybrid system propels the vehicle utilizing only stored electrical energy and the engine is turned off. The tractive torque is supplied from the motor, the generator, or a combination of both. This is the preferred mode when the desired power is low enough that it can be produced more efficiently by the electrical system than by the engine and when the battery is sufficiently charged. This is also a preferred mode for reverse driving because the engine cannot provide reverse torque to the power train in this configuration.
In the parallel hybrid mode, the engine is operating and the generator is locked. By doing this, a fixed relationship between the speed of the engine and the vehicle speed is established. The motor operates as either a motor to provide tractive torque to supplement the engine""s power, or can be operated to produce electricity as a generator. This is a preferred mode whenever the required power demand requires engine operation and the required driving power is approximately equal to an optimized operating condition of the engine. This mode is especially suitable for cruising speeds exclusively maintainable by the small internal combustion engine fitted to the hybrid electric vehicle.
In a positive split hybrid mode, the engine is on and its power is split between a direct mechanical path to the drive train and an electrical path through the generator. The engine speed in this mode is typically higher than the engine speed in the parallel mode, thus deriving higher engine power. The electrical energy produced by the generator can flow to the battery for storage or to the motor for immediate utilization. In the positive split mode, the motor can be operated as either a motor to provide tractive torque to supplement the engine""s power or to produce electricity supplementally with the generator. This is the preferred mode whenever high engine power is required for tractive powering of the vehicle, such as when high magnitude acceleration is called for, as in passing or uphill ascents. This is also a preferred mode when the battery is charging.
In a negative split hybrid mode, the engine is in operation and the generator is being used as a motor against the engine to reduce its speed. Consequently, engine speed, and therefore engine power, are lower than in parallel mode. If needed, the motor can also be operated to provide tractive torque to the drive train or to generate electricity therefrom. This mode is typically never preferred due to increased losses at the generator and planetary gear system, but will be utilized when engine power is required to be decreased below that which would otherwise be produced in parallel mode. This situation will typically be brought about because the battery is in a well charged condition and/or there is low tractive power demand. In this regard, whether operating as a generator or motor, the torque output of the generator is always of the same sense (+/xe2x88x92); that is, having a torque that is always directionally opposed to that of the engine. The sign of the speed of the generator, however, alternates between negative and positive values depending upon the direction of rotation of its rotary shaft, which corresponds with generator vs. motor modes. Because power is dependent upon the sense of the speed (torque remains of the same sense), the power will be considered to be positive when the generator is acting as a generator and negative when the generator is acting as a motor.
When desiring to slow the speed of the engine, the current being supplied to the generator is changed causing the speed of the generator to slow. Through the planetary gear set, this in turn slows the engine. This effect is accomplished because the resistive force acting against the torque of the generator is less at the engine than at the drive shaft which is connected to the wheels and is being influenced by the entire mass of the vehicle. It should be appreciated that the change in speed of the generator is not equal, but instead proportional to that of the engine because of gearing ratios involved within the connection therebetween.
In conventional vehicles, the cooling system has a variety of components that require cooling by a fluid cooling system, radiator and fan. Fluid cooled components typically include the engine and transmission. A fluid coolant circulates through a closed cooling loop, passes through each component to absorb heat, and then passes through the radiator. The radiator exposes the coolant to the fan""s airflow and releases the heat. A controller monitors engine and transmission temperatures and adjusts fan speed to maintain acceptable coolant temperature for the cooling loop. In addition to the fluid cooled components, the air conditioning (A/C) condenser requires cooling from airflow that comes from the fan(s) to keep the A/C compressor head pressures at acceptable levels.
In electric and hybrid electric vehicles the high voltage system and other electronic components unique to such vehicles require cooling. However, the conventional cooling system described above does not provide an appropriate temperature differential to remove the heat which builds up in the electronic components. Therefore a separate cooling system is commonly used to cool the electronic components of an electric or hybrid electric vehicle.
For example, in a typical hybrid electric vehicle, a DC/AC inverter and a DC/DC converter require cooling below the temperature range typically found in conventional internal combustion engine cooling systems. Without an adequate cooling system, the build up of the heat load during operation of a converter and/or an inverter threatens the operation and efficiency of these electrical devices as well as the operation of the vehicle itself. The present approach to eliminate or at least reduce heat build up includes the use of a separate radiative cooling system with a liquid coolant temperature significantly lower than the liquid coolant used to cool an internal combustion engine of a vehicle.
Even with use of a separate cooling system for the inverter and/or converter, the electrical components are threatened by the build up of heat during hot ambient conditions or extreme operating conditions. When such conditions occur, the present electronics cooling strategy calls for the electronic device to monitor its own temperature and shut down thereby preventing damage due to overheating. Such shut downs deprive the user of a fully functional hybrid electric vehicle.
Several deficiencies associated with the use of known hybrid electric vehicle designs and methods of operating the same have been described hereinabove. Several inventive arrangements and methods for operating hybrid electric vehicles are described hereinbelow that minimize, or remedy these deficient aspects of known designs, and/or provide benefits, in and of themselves, to the user. These new, improved and otherwise potentiated solutions are described in greater detail hereinbelow with respect to several alternative embodiments of the present invention.
In one aspect, a cooling arrangement for electronic components in a hybrid electric vehicle is disclosed. The arrangement includes an electronics cooling loop aboard a hybrid electric vehicle in which a DC/DC converter, DC/AC inverter and an electronics radiator are fluidly connected to each other to cool the converter and inverter. In a preferred embodiment, a electronics radiator fan is positioned near the electronics radiator to cause or enhance air flow across the electronics radiator. In yet another embodiment, a coolant pump is fluidly connected to the electronics cooling loop to cause fluid circulation. A temperature sensor in the cooling loop senses a temperature which is communicated to a supervisory module. The temperature sensor may be located at or near a cooling inlet of the DC/DC converter or between the DC/DC converter and DC/AC inverter. Based on the temperature input, the supervisory module controls the operation of the DC/DC converter. In a preferred embodiment, the supervisory module controls the DC/DC converter based on ambient outside temperature, radiator fan speed, air conditioning system operational modes, lighting system operation modes, and battery system energy capacity. By controlling the operation of the DC/DC converter, the heat contribution from the converter to the electronic cooling loop can be reduced or eliminated. While the DC/DC converter is shut down to reduce or eliminate the heat load of the electronics cooling system, electrical power can be supplied by the 12-volt battery and/or a conventional alternator driven by the internal combustion engine. In a preferred embodiment, the DC/DC converter is located upstream of the DC/AC inverter in the electronics cooling loop.
In yet another preferred embodiment, the supervisory module further controls the operating capacity of the DC/AC inverter based on the temperature in the electronics cooling loop. The supervisory module""s control over the DC/AC inverter allows the operating capacity of the inverter to be varied in response to a temperature of the electronics cooling system, thereby varying the heat contribution from the inverter to the electronics cooling loop. By reducing the operational capacity of the inverter, a corresponding heat load reduction occurs in the electronics cooling loop, thereby extending the duration of operating the hybrid electric vehicle under extreme operating scenarios and especially in hot ambient environments.
In another aspect, a method of controlling a cooling arrangement for electronic components in a hybrid electric vehicle is disclosed. In the most basic form, the method of control includes arranging an electronics cooling loop aboard a hybrid electric vehicle in which a DC/DC converter, DC/AC inverter and an electronics radiator are placed in fluid connection with each other to cool the converter and inverter, sensing a temperature in the electronics cooling loop, and selectively operating the DC/DC converter based on the sensed temperature in the electronics cooling loop. A preferred method of control includes controlling a pump that is fluidly connected to the electronics cooling loop for varying fluid flow, and controlling an electronics radiator fan, which in operation, causes air flow across the electronics radiator. In addition to, or apart from the control methods described above, selective operation of the DC/DC converter is based upon the cooling loop temperature sensed, ambient outside temperature, lighting system operational modes, and battery system energy capacity. As well as controlling the DC/DC converter to alter the heating load of the cooling loop, the speed of the electronics radiator fan can be controlled. In addition to or apart from the control methods described above, selective variation of the DC/AC inverter""s operating capacity occurs based upon the temperature sensed in the electronics cooling loop. As can be appreciated by those skilled in the art, the basic and alternative methods of controlling the converter and/or the inverter, as set forth, reduces the heat load of the electronics cooling loop. In doing so, a smaller electronics radiator can be utilized thereby saving on space and weight in the hybrid electric vehicle.
The general beneficial effects described above apply generally to the exemplary descriptions and characterizations of the devices, mechanisms and methods disclosed herein. The specific structures and steps through which these benefits are delivered will be described in detail hereinbelow.